1. Field of the Invention
The present invention relates to a power block including power semiconductor chips sealed or encapsulated with a transfer molding resin, and to a power semiconductor module using such a power block.
2. Background Art
Power blocks are used to control the current supplied to a load. In a typical construction of a power block, power semiconductor chips, electrodes, etc. are bonded to conductive patterns on an insulating substrate, and these components are encapsulated with a resin as necessary. It should be noted that the power semiconductor chips are, e.g., IGBTs or freewheeling diodes.
In order to protect the environment, SnAgCu- or SnAgCuSb-based lead-free solders are sometimes used instead of lead-containing solders to bond power semiconductor chips and electrodes to conductive patterns. However, devices using lead-free solder are known to have lower temperature cycling resistance than devices using lead-containing solder. One conventional practice to provide sufficient temperature cycling resistance to a structure using lead-free solder is to place it in a mold and encapsulate it by transfer molding. The resulting structure (i.e., a power block) has sufficient temperature cycling resistance, since it is covered with a transfer molding resin.
When a power block is transfer molded, the electrodes of the power block are sandwiched between the upper and lower molds so that these electrodes extend outwardly through and beyond the resin. This means that in resin-transfer-molded power blocks, the electrodes extend parallel to the surface of the insulating substrate.
On the other hand, power blocks manufactured without using transfer molding are typically constructed so that their electrodes extend upwardly from the top surface of the insulating substrate in order to reduce the mounting area. It should be noted that the exposed ends of the electrodes of power blocks are preferably located at such positions that the power blocks can be interchangeable with one another regardless of the way they are produced. However, since power blocks using lead-free solder must be transfer molded, they cannot be constructed so that the electrodes extend upwardly from the top surface of the insulating substrate. Therefore, it has been difficult to ensure interchangeability between transfer-molded power blocks using lead-free solder and power blocks manufactured without using transfer molding. This lack of interchangeability between these power blocks is likely to lead to a lack of interchangeability between the power semiconductor modules containing them.